size is 5.35 nm, which is the lower limit of the effective pore size. Third, large-scale hydraulic fracturing can improve the unconnected pores with the size more than 5.35 nm, so effective development of shale gas will be realized. Fourth, after hydraulic fracturing stimulation, the unconnected pores can increase the storage space of fracturing fluid in the matrix, absorb the fracturing fluid in the fractures, replace the shale gas in the pores and promote the automatic alleviation of water lock in shale gas reservoirs, so the single-well shale gas production will be increased. In conclusion, fluid occurrence and pore system in shale pores can be quantitatively divided by means of centrifugal + gradual temperature drying method combined with NMR experiments, movable water and capillary bound water can be determined by the high speed centrifugal + NMR experiments, and capillary bound water and clay bound water can be determined by the gradual drying + NMR experiments.

Zhang, K., Jia, C., Song, Y., Jiang, S., Jiang, Z., Wen, M., Huang, Y., Liu, X., Jiang, T., Peng, J., Wang, X., Xia, Q., Li, B., Li, X., Liu, T., 2020. Analysis of Lower Cambrian shale gas composition, source and accumulation pattern in different tectonic backgrounds: A case study of Weiyuan Block in the Upper Yangtze region and Xiuwu Basin in the Lower Yangtze region. Fuel 263, 115978.

http://www.sciencedirect.com/science/article/pii/S0016236119313304 Marine shale gas exploration in southern China has successes and failures. Under the condition of great hydrocarbon generation material basis, shale gas wells drilled from some shale gas blocks are rich in methane, while the wells in other shale gas blocks with high nitrogen and low hydrocarbon gas, which indicates that they have different accumulation mechanisms. Therefore, the study of gas composition in shale will help us to figure out the mechanism of shale gas accumulation and loss. In this paper, the Lower Cambrian shale from Wei-201 well in Upper Yangtze Weiyuan Block and Jiangye-1 well from Lower Yangtze Xiuwu Basin are selected as research object, and shale samples are used for tests and experiments including analysis of gas composition and nitrogen isotope, test of porosity and TOC content, overburden permeability test, permeability test before and after methane adsorption under different osmotic pressure, permeability test parallel and vertical to the bedding surface, FIB-SEM (Focus Ion Beam Scanning Electron Microscope) and FIB-HIM (Focused Ion Beam Helium Ion Microscope). Finally, the reasons for the difference in the gas components of the Lower Cambrian shale gas in Weiyuan Block and Xiuwu Basin are studied by means of seismic interpretation, core description and outcrop observation besides the tests and experiments. The results show that the gas components of the Lower Cambrian shale in Weiyuan Block, the Upper Yangtze, mainly consist of methane, derived from liquid hydrocarbon cracking. The sealing capacity of roof and floor, the great self-sealing of shale and the flat anticline structure contribute to the high methane content in shale gas. The Lower Cambrian shale gas in Xiuwu Basin, the Lower Yangtze, is mostly nitrogen, which is derived both from atmosphere and deep crust-upper mantle. The detachment layer at the bottom of the Lower Cambrian, the widely developed deep faults and the Jurassic volcanic activity are the reasons for the high nitrogen and low hydrocarbon of shale gas. Based on the above analysis, the patterns are summarized for shale gas accumulation in the simple anticline background and reservoir destruction in the complex syncline background.

Zhang, M., Zhang, W., Cheng, Q., Yuan, Q., 2020. Geochemical characteristics and significances of C -C short- 19 26 chain steranes in crude oils from the Western Qaidam Basin, China. Arabian Journal of Geosciences 13, 106.

https://doi.org/10.1007/s12517-020-5074-9 Based on biomarker analysis of crude oils from Western Qaidam Basin, the geochemical characteristics and significances of C -C short-chain steranes were investigated. The oils are characterized by unimodal n-alkane 19 26 distributions with even (C -C ) predominance, low Pr/Ph (mostly < 0.5), high concentration of gammacerane, 18 24 and the C -hopane over the C -hopane, suggesting high salinity and anoxic conditions typical of a saline 35 34 lacustrine sedimentary environment. The short-chain steranes, comprising C sterane, C pregnane and C 19 21 22 homopregnane as well as C -C steranes were detected in these crude oils. The relative abundance of these 23 26 individual compounds showed positive correlations; especially C pregnane and C homopregnane were found 21 22 to be closely correlated with other short-chain steranes. On the other hand, the C sterane displayed general 25 correlation with other short-chain steranes, whereas the C sterane exhibit relatively poor correlation. The study 26 of short-chain sterane distributions and of other aliphatic and aromatic compounds indicated that the relative concentration of short-chain steranes within the study area is controlled by multiple factors such as redox